ANTHROPOGENIC CHLOROFLUOROMETHANES AND SEASONAL MIXING RATES IN THE MIDDLE ATLANTIC BIGHT

Measurements of the chlorofluorocarbons (CFCs), F11 (CCl3F) and F12 (C Cl2F2) were made during the Shelf Edge Exchange Processes II (SEEP-IT) experiment in the Middle Atlantic Eight during 1988-1989. These compo unds undergo large seasonal variations in surface water concentration as a result of temperature-induced solubility changes. Outgassing in s ummer produces vertical concentration gradients that can be exploited to estimate a cross-pycnocline vertical eddy-diffusivity suitable for biogeochemical flux calculations. Model results based on an explorator y study suggest an average K-2 of 1 x 10(-5) m(2) s(-1) for this regio n during the stratified period. CFCs have advantages over other budget approaches for studying mixing processes, including heat budgets, as there are no internal sources or sinks other than air-sea gas exchange . In order to exploit further the CFC budget of sub-pycnocline shelf w aters, regular cruises through the summer months and characterization of CFC levels at the time of stratification are required.